1. Technical Field
The invention generally relates to three phase delta power distribution systems and more particularly, relates to ground referencing of a delta power system.
2. Background Art
The three phase delta power distribution system is well understood in the field of power engineering and its lack of a ground reference has been both beneficial and a hindrance to operation. There are advantages to having an electrically unreferenced or floating power distribution system. For a fault current or short to occur, two different phase conductors need to be connected to ground simultaneously. The design is tolerant to single faults which reduces the risk of system outages in critical applications. If one leg of the power source is accidentally faulted to ground, the power system can continue to operate without outage or equipment damage.
Delta power system repairs for this type of problem can be deferred until a time period can be set aside for such maintenance. Because there is no major impact to the operation of equipment due to an insulation failure of the conductor wires at a single point, faults can exist without being detected. This poses a risk as a second fault will immediately bring the whole delta power supply system down without warning. This running or hidden failure condition can remove the element of security provided by a delta power system.
Three phase delta power sources have no neutral reference point to allow monitoring individual phase polarity or phase zero voltage crossing points. A synthetic reference point can be created by averaging the three phase line voltages in time to simulate a center voltage point. The synthetic reference point provides a value that approximates the center point of the delta voltage source unless there is an imbalance in the load current.
Errors in the value of the synthetic reference point occur as a result of distortion in phase voltage amplitude due to imbalanced source or load conditions. In circuits detecting the passage of a phase voltage through a ground reference level, any electrical dislocation to the ground point becomes a very significant source for errors. As a detector circuit increases in sensitivity, the greater is the need for a stable and accurate reference ground point.
What is needed is a way to provide a hard centered voltage point within a delta power distribution system. Application of a voltage centering system within a delta power supply allows electrical equipment to be connected by a specific impedance to a reference plane such as earth potential or ground. Electrically anchoring a delta power system to a grounding point allows greater system integrity and safety. With a centered reference voltage, full wave line rectification is possible for a delta power source.